Garner, 46, showed she can pack hard punches and kicks, while deftly handling firearms, for the thriller Peppermint (opening Sept. 7). The film dropped its first trailer Thursday, with this image of Garner showing off her action-star biceps.

Garner plays a loving mother frustrated that the system won't lock up a drug cartel that killed her family. So her Riley North spends five years training to become an assassin and takes matters into her own hands.

Garner told a CinemaCon audience in April that she was pumped to return to the kind of action shape she was in when breaking out as a TV superstar in 2001's Alias.

She said working on Peppermint with director with Pierre Morel, who made Liam Neeson an action hero with Taken, provided the incentive to return to action.

Jennifer Garner kicks it in "Peppermint."(Photo: STX)

"There is no bigger stakes than your children," said Garner, the mother of three kids with ex Ben Affleck. "This was to avenge your child's death, and there's no bigger reason to go out and get into really good shape and then kill people."

To get in fighting shape, Garner said she doubled her daily workout, adding boxing and martial arts to the mix. She gave her fans a look at her workout world on Instagram.